1. Field of the Invention
The present invention relates to a printer and, more particularly, to a printer incorporating a daisy type wheel and other associated parts.
2. Detailed Description of the Prior Art
The printer of this type proposed hitherto incorporates a hammer opposing a type head and a magnet for actuating the hammer. The armature of the hammer is required to operate with a predetermined constant stroke. A plurality of parts such as the hammer, hammer frame, armature, magnet and so forth are necessary for achieving such function of the hammer. Although a stopper for limiting the stroke of the armature is disposed in an adjustable manner, there are a plurality of points of adjustment for these parts, and these points of adjustment are related to one another to make the adjusting work troublesome and difficult. Major points of adjustment are, for instance, the position of the hammer relative to the type head, stroke of the hammer, position of the hammer in relation to the armature, range of operation of the hammer, position of the magnet in relation to the armature and so forth. Therefore, in the conventional printer, the adjustment of the hammer actuating mechanism constitutes a bottleneck in the assembling process.
In the conventional magnet device for actuating the hammer, there is provided an armature for imparting driving power to the other parts of the device. This armature is attached to a substrate to which a coil wound around a core is secured. Thus, the magnet device is constituted by the substrate, coil and the armature which are integrated by bolts or like means. Therefore, highly troublesome work is required for setting the positions of these parts in relation to the others. In the case where a stopper is provided for setting the position of the armature and the range of rotation of the same, the adjustment of the stopper poses another problem.
Furthermore, in the printer incorporating a daisy type wheel, types are arranged on two concentric circles to provide printing of characters the number of which is twice as large as the number of fingers, by changing the position of the type wheel in relation to the hammer. In this case, the drive shaft to which the type wheel is secured is coupled to a motor through a universal joint to permit the displacement of the drive shaft axis, and an arm is connected at its one end to the drive shaft while the arm is positioned horizontally and rotatably held at its base portion. A pair of magnets disposed above and below the arm are selectively energized to rotate the arm to thereby shift the type head up and down. In order to bias the arm to the neutral position, two coiled springs are stretched and connected to the upper and lower sides of the arm.
Since these coiled springs are required to exert a certain tensile force even when the arm is rotated, these coiled springs are held in the stretched condition when the arm takes the neutral position. Thus, the setting of the arm at the neutral position is made more difficult due to fluctuation of the coiled springs. In order to avoid an undue influence on the shifting characteristic, it is necessary to utilize a step of making an adjustment in the assembling process. When the arm is rotated, the force for biasing the arm is materially given by these two coiled springs. Although the spring forces act to negate each other, the spring constants are added to each other to increase the rate of change of load in relation to the deflection amount. This in turn requires a magnet having a capacity large enough to drive this arm.
In the printer having a daisy type wheel, a carriage by which the type head is carried is held in such a manner as to be able to pivot or tilt, to thereby facilitate the replacement of the type head. Hitherto, there have been two types of holding mechanisms for holding the type wheel: namely a mechanism of the type in which the operative position and release position are set manually by means of a lever and a latch and a mechanism of the type in which the carriage is set either at the operative position or release position by means of a toggle mechanism. In the first mentioned type, a serious accident may occur when the operator forgets to manually lock the type head after the attaching of the same, so that great care is required in the use thereof. In the second mentioned type, although the carriage can be set by a simple operation of making the carriage pivot or tilt, the carriage is liable to be floated or displaced or oscillated during use by the vibration and impact generated at the time of printing, because the carriage in the set position is held solely by the toggle spring.
From another point of view, in the printer having a daisy or like type wheel mounted replaceably, the carriage held by a carrier and adapted to utilize a reciprocating motion is mounted so as to be able to pivot or tilt, and a fulcrum of rotation is formed on the carriage. In addition, the carriage must be precisely located also in the direction of the reciprocating motion. Therefore, in the conventional printer, both side surfaces of the carriage are polished to provide a highly precise distance between both side surfaces so that an assembly is performed with high precision making use of these side surfaces as the reference surface. Therefore, it is necessary to machine the main body with high precision. In addition, the mounting of the carriage on the carrier has to be performed by axially aligning two shafts projecting inwardly from the carrier. It is often experienced that the smooth rotation of the carriage fails due to a misalignment of the axes or a local contact between the carriage and the carrier.
In the conventional printer having a type head, a ribbon cartridge containing an ink ribbon is detachably secured to the carriage carrying the type head. In order to enable the operator to visibly check the character immediately after the printing, the ink ribbon is raised to the printing position only during the printing, while it is lowered when printing is not occurring. Hitherto this function has been achieved by allowing a mounting plate, to which the ribbon cartridge is attached, to tilt vertically within a predetermined range of angle. The attaching plate, however, has a considerably large weight, so that the device for causing the vertical tilting motion of the attaching plate is required to have a larger power. In addition, the attaching plate having the large weight generates a vibration of large magnitude during the operation thereof.